[[image:RBG-LED.jpg|thumb|right|250px|Blue, green, and red LEDs; these can be combined to produce most perceptible colors, including white.
Infrared and ultraviolet (UVA) LEDs are also available.]]
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[[image:RBG-LED.jpg|thumb|right|250px|Blue, green, and red LEDs; these can be combined to produce most perceptible colors, including white.
Infrared and ultraviolet (UVA) LEDs are also available.]]
A light-emitting diode (LED) ( ), is a semiconductor diode that emits light when an electric current is applied in the forward direction of the device, as in the simple LED circuit. The effect is a form of electroluminescence where incoherent and narrow-spectrum light is emitted from the p-n junction.
LEDs are widely used as indicator lights on electronic devices and increasingly in higher power applications such as flashlights and area lighting. An LED is usually a small area (less than 1 mm2) light source, often with optics added to the chip to shape its radiation pattern and assist in reflection. The color of the emitted light depends on the composition and condition of the semiconducting material used, and can be infrared, visible, or ultraviolet. Besides lighting, interesting applications include using UV-LEDs for sterilization of water and disinfection of devices,Development of a new water sterilization device with a 365 nm UV-LED, Medical and Biological Engineering and Computing, Volume 45, Number 12 / December, 2007 and as a grow light to enhance photosynthesis in plants.
Discovery and development
The first known report of a light-emitting solid-state diode was made in 1907 by the British experimenter H. J. Round of Marconi Labs. Russian Oleg Vladimirovich Losev independently created the first LED in the mid 1920s; his research, though distributed in Russian, German and British scientific journals, was ignored, and no practical use was made of the discovery for several decades. Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955. Braunstein observed infrared emission generated by simple diode structures using GaSb, GaAs, InP, and Ge-Si alloys at room temperature and at 77 K. In 1961, experimenters Bob Biard and Gary Pittman working at Texas Instruments, found that gallium arsenide gave off infrared radiation when electric current was applied. Biard and Pittman were able to establish the priority of their work and received the patent for the infrared light-emitting diode.
The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr., while working at General Electric Company. He later moved to the University of Illinois at Urbana-Champaign. Holonyak is seen as the "father of the light-emitting diode". M. George Craford, a former graduate student of Holonyak's, invented the first yellow LED and 10x brighter red and red-orange LEDs in 1972.
